AQA Biology (Combined Science) Unit 5: Homeostasis Knowledge Organiser
Coordination Centres
Brain: coordinates information from receptor
cells and sends signals to muscles and glands
Spinal Cord: coordinates messages from brain
and receptor cells and coordinates reflexes
Pancreas: coordinates glucose levels in blood
Keywords
Central Nervous System (CNS) – Brain and spinal cord
Effectors – Muscles or glands that bring about
responses in the body
Homeostasis – Regulation of the internal conditions of
a cell or organism to maintain optimum conditions, eg.
blood glucose, body temperature, water level
Nerve – Bundle of hundreds or thousands of neurones
Neurone – A single nerve cell
Receptors – Cells that detect stimuli
Reflex Arc – Bring about a reflex action
Stimulus – A change in the environment
Synapse – Gap between two neurones
Receptor Cells
Neurones
The nervous system allows a fast, short-lived response
to a stimulus.
Sensory Neurone: carries impulses from receptors to
CNS
Relay Neurone: connect sensory neurones to motor
neurones
Motor Neurone: carries impulses from CNS to effectors
The axon is a long stretched-out fibre of cytoplasm
which the electrical impulses pass along. Some axons
are surrounded by a myelin sheathe which insulates
the impulse. The branched endings, dendrites, connect
neurones together with synapses to create a network.
Synapse
When an electrical impulse reaches the end of a neurone, a
chemical (neurotransmitter) is released across the gap.
The chemical diffuses across the synapse.
When the chemical reaches the next neurone this starts
another electrical impulse.
Skin- touch, pressure, pain, temperature
Retina in eye- light intensity,
colour
Nose- chemicals
in air
Tongue- chemicals in
food
Ear- sound
Nervous Pathway
A stimulus is detected by receptors and
information passes along neurones (nerve cells)
as electrical impulses to the Central Nervous
System.
The CNS coordinates the response of effectors.
STIMULUS RECEPTOR COORDINATOR
EFFECTOR RESPONSE
Reflex Arc
Reflexes are automatic and rapid. They do not
involve the conscious part of the brain and travel
through the closest part of the CNS
The path a reflex action takes is called a reflex arc
They only use three neurones.
Reflex actions are important as they protect the body
from harm
AQA Biology (Combined Science) Unit 5: Homeostasis Knowledge Organiser
Negative Feedback
Negative feedback loops work to maintain a steady
state. If a level rises too high or too low, changes takes
place to return the level to its normal level.
Negative feedback of thyroxine:
Endocrine System
Compared to the nervous system, the effects of the
endocrine system are slower but act for longer. Pituitary Gland
Called the master gland because it produces a lot
of different hormones that act on other glands.
Eg. FSH and LH produced by the pituitary gland
act on the ovaries
Controlling
Blood
Glucose
Keywords
Adrenaline – Hormone produced by the adrenal glands
to increase heart and breathing rate – ‘flight or fight’
Diabetes – A condition where someone cannot
regulate their blood sugar concentration
Endocrine System – made up of glands which secrete
hormones directly into the bloodstream
Glucagon – Hormone released by the pancreas when
blood glucose level is too low
Glycogen – Store of carbohydrate (glucose) in animals
Hormone – Chemicals, released from glands, that
travel in the blood to a target organ
Insulin – Hormone released by the pancreas when
blood glucose level is too high
Thyroxine – Hormone produced by thyroid gland to
control metabolic rate
Diabetes
Type 1:
Develops in childhood
Pancreas fails to produce insulin
Lack of insulin causes uncontrolled high blood sugar
levels
Normally treated with insulin injections
Type 2:
Develops in adulthood, due to diet, obesity and lack
of exercise
Body no longer responds to insulin
Normally treated with controlled diet and exercise
AQA Biology (Combined Science) Unit 5: Homeostasis Knowledge Organiser
Hormones in the Menstrual Cycle
.
Keywords
Contraception – Methods of preventing pregnancy
Embryo – Collection of cells developed from a fertilised egg
Fertilisation – The nucleus of a sperm cell combining with
the nucleus of an egg cell
Menstruation – Loss of the lining of the uterus through the
vagina (a period)
Oestrogen – The main reproductive hormone in females,
produced by the ovaries to stimulate ovulation (at around
day 15)
Ovulation – The release of an egg from the ovaries every 28
days
Testosterone – The main reproductive hormone in males,
produced in the testes to stimulate sperm production
Menstrual Cycle
The menstrual cycle occurs in females, approximately
every 28 days. It is a cyclical process of the building of the
lining of the uterus and ovulation.
If the egg is fertilised by a sperm, then pregnancy follows.
If the egg is not fertilised, the lining of the uterus is lost
and leaves the body as the menstruation (or period).
It is controlled by four main hormones.
Contraception
The Pill – oral contraceptives that contain oestrogen
to inhibit FSH production so no eggs mature
Injection, implant or skin patch – slow release of
progesterone to inhibit ovulation for a number of
months of years
Spermicides – chemicals that kill sperm
Barrier methods (condom/diaphragm) – prevent
sperm reaching the egg
Intrauterine devices (the coil) – release hormones or
prevent a fertilized egg implanting in the uterus lining
Abstinence – not having intercourse
Sterilisation/vasectomy - surgical methods of male
and female sterilisation
Infertility
If a woman has naturally low levels of
FSH and LH she can be given a fertility
drug containing these hormones and
become pregnant naturally.
If this does not work, then In Vitro
Fertilisation (IVF) may be used:
1. Mother is given FSH and LH to stimulate
production of many eggs
2. Eggs are collected from the ovaries and
fertilised by the father’s sperm in the lab.
3. Fertilised eggs divide into embryos.
4. One or two embryos are inserted into the
mother’s uterus
Problems with IVF
Emotionally and physically
stressful
Low success rate
Multiple births
Complications during
pregnancy or birth
Premature (early) or
underweight babies born
AQA Biology (Separate Science) Unit 5: Homeostasis Knowledge Organiser
The Brain
Cerebral cortex – Intelligence,
language, memory and
consciousness
Cerebellum – Voluntary
coordination of muscles
Medulla – Involuntary
coordination, such as
breathing, heart rate and swallowing
Keywords
Accommodation – changing the shape of the
lens of the eye to focus on near or distant
objects
Hyperopia – long sightedness (cannot focus
on near objects)
Myopia – short sightedness (cannot focus on
distant objects)
Studying the Brain
The complexity and delicacy of the brain makes it difficult to
study and treat brain disorders.
Studying patients with brain damage: damage to different
brain areas produce different behavioural and psychological
effects
Electrical stimulation: stimulating different parts of brain and
analysing brain wave patterns can identify what each area
does
Magnetic Resonance Imaging (MRI): uses strong magnetic
fields and radio waves to produce detailed images of the brain
and spinal cord, eg. detecting cancerous cells
The Eye
The eye is a sense organ containing receptors
sensitive to light intensity and colour
Accommodation
Distant object Near object
Ciliary muscles relax Ciliary muscles contract
Suspensory ligaments Suspensory ligaments
pulled tight loosen
Lens pulled thin to only Lens thickens to
slightly refract rays strongly refract rays
Eye Problems
Myopia: If the eyeball is too long
then light rays are focused in front
of the retina. Can be corrected with
concave lenses.
Hyperopia: If the eyeball is too
short then light rays focus behind
the retina. Can be corrected with
convex lenses.
Correcting Vision
Contact lenses: sit on the cornea to refract the light rays
Laser surgery: lasers used to change the shape of the cornea
Lens replacement surgery: Artificial lens implanted into eye
AQA Biology (Separate Science) Unit 5: Homeostasis Knowledge Organiser
Keywords
Anti-Diuretic Hormone (ADH) – Hormone
released by the pituitary gland that tells the
kidneys to reabsorb more water
Deamination – Removal of an amino group
from amino acids
Hypothalamus – Thermoregulatory
(temperature controlling) centre of the brain
Urea – A toxic waste product produced when
proteins are broken down
Vasoconstriction – Narrowing of blood vessels
in response to cold
Vasodilation – Widening of blood vessels in
response to heat
The Brain
Water and Nitrogen Balance
Lungs – water lost during exhalation
Sweat – water, ions (sodium, potassium, calcium,
nitrogen) and urea lost
Urine – excess water, ions and urea removed via the
kidneys
The Kidney
Kidneys filter the blood to form urine.
Each kidney contains
millions of kidney
tubules (nephrons)
partly in the cortex
and partly in the
medulla.
The kidneys filter the blood to remove any
substances that are in excess or that are not
needed by the body.
All of the glucose is reabsorbed into the
blood. Some of the water and ions are
reabsorbed depending on what is needed –
selective reabsorption.
Controlling Body Temperature
Human body temperature is 37°C – the optimum for
enzyme activity.
The hypothalamus detects blood temperature. The skin
contains temperature receptors to send impulses to the
hypothalamus.
If body temperature is too low: blood vessels constrict,
sweating stops and muscles contract (shiver)
If body temperature is too high: blood vessels dilate and
sweat is produced to release heat to the air.
Controlling Water Levels
Water levels of blood are monitored by the
pituitary gland.
It releases Anti-Diuretic Hormone (ADH).
ADH causes the kidney tubules to become
more permeable and reabsorb more water.
This is an example of negative feedback.
AQA Biology (Separate Science) Unit 5: Homeostasis Knowledge Organiser
Keywords
Auxin – Plant hormone that controls the responses
of plants to light and gravity
Dialysis – The process of cleansing the blood
through a dialysis machine
Diffusion – movement of substances from a high
to a low concentration
Gravitropism/Geotropism – Plant growth in
response to gravity
Kidney Failure – A medical condition where the
kidneys no longer work properly
Negative tropism – Away from the stimulus
Phototropism – Plant growth in response to light
Positive Tropism – Towards the stimulus
Dialysis or Transplant
Kidney Dialysis
Dialysis restores the concentrations
of substances in the blood to normal
levels and has to be carried out
regularly.
1. Blood high in urea flows between
partially permeable membranes in
the opposite direction to dialysis fluid
(maintain concentration gradient)
2. Dialysis fluid has the same
concentration of glucose and ions as a
healthy person
3. Only excess ions and urea move
out of the blood by diffusion.
Plant Hormones – Phototropism
Auxin is produced just behind the tip of the
shoot.
It moves to the shaded side of a stem.
Cells on the shaded side elongate and the
shoot bends towards the light
Kidney Transplant
A diseased kidney is replaced by a
healthy donor kidney.
Rejection: The donor must be a
similar tissue type to the recipient
and immunosuppressant drugs
are given to stop the immune
system attacking the new kidney.
Plant Hormones – Gravitropism
Auxin is produced just behind the tip
of the root.
It moves to the lower side of the root
due to gravity.
In roots, auxin inhibits cell elongation
and roots grow downwards
Using Plant Hormones
Giberellins: Initiate seed germination
Used to end seed dormancy, promote flowering, increase fruit size
Ethene: Controls fruit ripening
Used in the food industry to control fruit ripening during storage
and transport
Auxins: Used as weed killers, rooting powders and promoting
growth in tissue cultures
Top Related